Dedicated Short-Range Communication (DSRC) road toll systems are standardised in ISO 14906 and EN 15509 standards, for example. DSRC communication at the radio interface can occur, for example, in accordance with the WAVE standard IEEE 1609.11. For security reasons, system-wide keys (master keys) are not stored in the onboard units (OBUs) in such DSRC road toll systems. Instead the OBUs receive only individual keys derived therefrom (derived keys). Only these individual keys are transmitted or used via the DSRC radio interface.
The derivation code required for this, referred to as “key diversifier” in the ISO 14906 and EC 15509 standards, represents an individual identifier for each onboard unit for the respectively used rule for derivation of the individual key (derived key) from the system-wide key (master key). According to the prior art, the derivation code (key diversifier) is notified in any communication between an onboard unit and a beacon from the onboard unit to the beacon, so that the latter can derive (emulate) the respective individual key of the onboard unit from the system-wide key “on the fly” for communication with or access to the onboard unit.
This configuration encompasses a data protection problem. Since in every DSRC radio communication the—onboard unit specific—derivation code is firstly transmitted from the onboard unit via the radio interface by tapping the radio interface or by targeted fraudulent readout of a passing onboard unit.